1. Field of the Invention
The present invention relates to a method for detecting abnormality in a parallel battery, and more specifically relates to a method for detecting abnormality in a parallel battery-connection circuit.
In this application, a plurality of secondary batteries connected in series is referred to as "a serial circuit," and a circuit in which a plurality of serial circuits are connected in parallel is referred to as "a parallel battery-connection circuit".
2. Description of the Related Art
In one use of secondary batteries, a plurality of secondary batteries are connected in series (serial circuit) so as to provide a high voltage, and a plurality of serial circuits are also connected in parallel so as to provide a high capacity. In order to detect a problem, e.g., an internal short-circuit occurring in such a secondary battery circuit, the following two methods have been proposed.
In one method, the voltage or current value in each serial circuit is monitored so as to compare voltages and current values between the serial circuits and detect a voltage drop or a current value rise caused by abnormality. A serial circuit may be divided into several blocks for a block-by-block complete monitoring. This method is, however, impractical because it requires a complicated apparatus, which may cause a high possibility of defects and dispersion in detected values.
The other method for detecting abnormality utilizes a current value rise of in a serial circuit including a secondary battery with a problem, e.g., overcharging or overdischarging. Specifically, the temperature of a serial circuit rises when the circuit includes a secondary battery with such a problem. Therefore, the abnormality detection in a parallel battery-connection circuit can be controlled based on the absolute value of the temperature values detected from the plurality of serial circuits.
However, the following problem arises if the abnormality detection in a parallel battery-connection circuit is controlled based on the absolute value of the temperature values detected from the plurality of serial circuits.
The temperature values of a plurality of serial circuits are prone to be affected by the environmental temperature outside the parallel battery-connection circuit. If the environmental temperature outside the parallel battery-connection circuit is high, the temperature values of the plurality of serial circuits will also become high.
Therefore, in the case where the environmental temperature outside the circuit is high, the temperature values detected from the serial circuits would rise even if there is no problem of overcharging or overdischarging the secondary batteries of the parallel battery-connection circuit. As a result, such a method of abnormality detection has a risk of resulting in an erroneous determination that an abnormality has been generated even if there is no problem in the parallel battery-connection circuit.